1. Field of the Invention
The invention relates to a method of straightening a stack of sheet material that has been deformed after being conveyed on a roller conveyor. The rollers of the conveyor are mounted so as to rotate about parallel axes of rotation extending transversely to the direction of conveyance of the stack. The invention also relates to a device for straightening a stack of sheet material deformed by being conveyed on a roller conveyor the rollers of which have parallel axes of rotation extending transversely to the direction of conveyance. Finally, the invention relates to use of the device for changing the direction of stacks of sheet material.
2. Brief Description of the Background Art
In factories for making cardboard packaging formed by folding cardboard blanks, for example corrugated cardboard, the stacks of cardboard blanks undergo various cutting, grooving, printing operations, etc. and consequently must be conveyed over relatively large distances from one place to another in the factory. To this end, stacks of cardboard blanks up to 1.5 to 2 meters and weighing several hundred kilograms, typically 500 to 750 kg, are conveyed by conventional roller conveyors.
Because of the pressure exerted on the sheets at the bottom of the stack, the rollers cause the sheet resting on them, particularly when the sheet is of corrugated cardboard, to creep and thus slow down the sheet relative to the rest of the pile. The creeping motion is gradually transmitted over a thickness of a few centimeters from the base of the stack, giving the stack a cross-section in the shape of an elephant's foot. The deformation of course depends on the distance traveled by the stack, so that it may finally be great enough to cause the stack to fall. Of course such a risk is a danger to the safety of plant personnel, in view of the weight and height of the stacks, and the fall of a stack will also be expensive in terms of production and possible damage to the actual blanks themselves.